I just bought CMax Energi. I have 40K km on 1.5 yr Kia Soul EV, so have some experience with pure EV.
I think the major issue/mistake/misunderstanding here is what plugin cars like CMax/Fusion Energi is and is NOT:
- Energi is NOT pure EV
- Energi is hybrid
Treating them like an EV and trying to avoid ICE activation is the main reason for most of the degradation issues. There are other factors that you cannot easily deal with it, in particular location. Leaf owners have documented degradation in different regions and it is VERY clear that it is much worse in warmer climates. Most of the problems were in hot states like Florida/Cali/Arizona. Not much you can do about that except look for liquid cooled cars.
Back to EV mode.
The common power term used is "C" which is relative to battery size.
Soul EV usable 27 kWh, so 1C = 27 kW
CMax usable 5.5 kWh, 1C = 5.5 kW
In GENERAL (to avoid complications regarding different LiIon chemistries, etc.) for LiIon batteries:
0 - 0.5C = easy, low load
0.5C - 1C = normal, moderate load
1C - 3C = high load
3+C = very high load
Keep in mind this is approximate scale, not meant to be super accurate, so don't worry about exact numbers!
Low speed driving in EVs is no big deal, so nothing to talk about. Instead what happens at 80 km/h and higher (over 45 mph).
Soul has real-time motor power readings, so I can tell you typical power. Although keep in mind its CD sucks, so CMax would usually pull bit less power due less air resistance.
When I am cruising around 90ish km/h (50ish mph) I can see power in the 10 kW to 15 kW range.
Now for Soul EV it is:
10 / 27 = 0.4C
15 / 27 = 0.6C
So using the scale we can say that Soul EV can maintain this cruising speed without breaking a sweat, pretty easy no issues. Indeed after 40K my degradation is less that 10%; didn't test it but from all readouts I don't see any significant range loss.
Applying the same to CMax:
10 / 5.5 = 1.8C
15 / 5.5 = 2.7C
Now you can see clearly that CMax battery has to work MUCH harder in EV mode to maintain this highway cruising speed. Keep in mind this fairly slow for highway, so our perception is that car is not working super hard. In fact the battery is working hard! At the top range you are actually coming close to very high load. If you add heat (warmer climate) and heavy reliance on EV mode you are pretty much creating perfect conditions for accelerated degradation.
Now other cars can do this bit better because they have liquid cooling and/or much higher capacity battery that can handle this load easily. Say Tesla 60 kWh pack would be 15 / 60 = 0.25C = super easy load
The mistake that Ford made here is to allow CMax EV mode to draw 10+ kW sustained. 10 kW burst would be fine for 10-20 seconds, but I would not allow it for a longer period. The battery is too small to handle it and avoid degradation.
Now we can be angry at Ford but to be fair most car companies are still learning and they are improving (slowly) over time.
In practice what it means for us is that you want to use EV Later mode any time you are going over 80 km/h, especially in summer.
The other point was brought up earlier and again is super important to understand:
Soul EV average 5 km/kWh, 40K km / 5 = 8K kWh / 27 kWh = 300 cycles (approximate)
CMax average 6 km/kWh, 40K km / 6 = 6666 kWh / 5.5 kWh = 1212 cyclec (approximate)
So for the same distance (40K km) which we generally think of as normal, no big deal, we can clearly see that CMax has to use A LOT more cycles than a pure EV. This is huge difference. 300 cycles is no big deal and I don't have much degradation. Teslas and other big pack EVs have even less cycles.
However for this small pack using EV mode only (mostly) you need a huge number of cycles. So it no surprise to see so much degradation. Again this is not EV car and should NOT be driver like EV car.
For all EVs one notable difference is that efficiency jumps a lot at lower speeds. For instance, you can get as much as 10 km/kWh at lower speeds say 40-50 km/h and it drops down to 3-4 kWh at higher speeds. In terms of cycles it means that battery has to be half as much cycles for a given distance as long as you limit its use to lower speeds.
In summary, to reduce degradation:
1) Limit EV use to low power levels (below 10 kW)
a) low speed driving
b) coasting at higher speed (glide)
c) always push ICE to handle acceleration as much as possible
2) Manage heat
a) avoid charging on hot days, charge at night
b) rest period between trips to allow cooling
For CMax I see EV mode as something to use on local roads with many stop signs and traffic lights. Also it can be useful for gliding. However on all 80 km/h and higher limit roads I am looking to use EV Later mode.